add encode and decode strings

Author: tg123

encode-and-decode-strings/Codec.java

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+Solution.java

encode-and-decode-strings/README.md

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+public class Codec {
+
+    static final int MAX_LEN = Integer.toHexString(Integer.MAX_VALUE).length();
+
+    // lazy ... should be byte[]
+    static final String NUM_PATTERN = "%0" + MAX_LEN + "x";
+
+    String serializeNumber(int n){
+        return String.format(NUM_PATTERN, n);
+    }
+
+    int deserializeNumber(char[] s, int offset){
+        return Integer.parseInt(new String(s, offset, MAX_LEN), 16);
+    }
+
+    /*  [count] [str len] [str  ...]             ... [str len][str  ...  ]
+     *  0       L         2L        2L + strlen      nL       (n + 1)L   (n + 1)L + strlen
+     */
+
+    // Encodes a list of strings to a single string.
+    public String encode(List<String> strs) {
+        StringBuilder sb = new StringBuilder();
+        sb.append(serializeNumber(strs.size()));
+
+        for(String s : strs){
+            sb.append(serializeNumber(s.length()));
+            sb.append(s);
+        }
+
+        return sb.toString();
+    }
+
+    // Decodes a single string to a list of strings.
+    public List<String> decode(String s) {
+        char[] S = s.toCharArray();
+
+        int offset = 0;
+        int n = deserializeNumber(S, offset);
+        // move to first str len start
+        offset += MAX_LEN;
+
+        ArrayList<String> strs = new ArrayList<>(n);
+
+        for(int i = 0; i < n; i++){
+
+            int len = deserializeNumber(S, offset);
+
+            // move to str start
+            offset += MAX_LEN;
+
+            strs.add(new String(S, offset, len));
+
+            // move to next str len start
+            offset += len;
+        }
+
+        return strs;
+    }
+}
+
+// Your Codec object will be instantiated and called as such:
+// Codec codec = new Codec();
+// codec.decode(codec.encode(strs));

encode-and-decode-strings/Solution.java

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+---
+layout: solution
+title: Encode and Decode Strings
+date: 2015-09-03 13:28:10+08:00
+leetcode_id: 271
+---
+{% include_relative README.md %}